Various methods of directly connecting components such as semiconductor chips to an electrode such as a circuit pad conductor formed on a package substrate, e.g., a printed circuit board (PCB), have been conventionally proposed and practiced. As one of these conventional methods, there has been disclosed a method of forming a projecting electrode, as shown in FIG. 25, which includes an upper layer 3a of gold or the like formed in a wafer state by a plating method and a lower layer 3b of solder or the like having an eutectic composition stacked on the upper layer 3a by a plating method (Japanese Laid-Open Patent Publication No. 9-97791).
After forming the electrode in this manner, the wafer is divided into individual semiconductor chips for use in a packaging process, and good chips alone undergo a subsequent procedure while defected chips are scrapped. In the packaging process, by using a semiconductor chip having the projecting electrodes on it, the projecting electrodes formed on the semiconductor chip 6 are positioned in accordance with electrodes 5 formed on the respective, receiving substrate 4. Then, the semiconductor chip 6 is connected to the electrode 5 of the package substrate 4, typically using flux and heating the structure in a reflow furnace.
However, since it is necessary to conduct the plating in a wafer state in this method, if the wafer includes a small number of good chips, the manufacturing unit cost per semiconductor chip becomes relatively higher, and hence, the method cannot always be practically adopted. Furthermore, when problems arise in the procedure for forming the projecting electrodes by the plating method, there is no recovering means. Therefore, the problematic wafer is unavoidably abandoned. In addition, since a wafer is divided into semiconductor chips after forming the projecting electrodes, a wafer having a defect caused in the dividing process is also discarded. Moreover, in the procedure for forming the projecting electrodes by the plating method, various metallic ions can often be mixed in the plating bath used. Therefore, impurities can be deposited in the upper and lower layers, possibly causing a connection failure.
Another technique is disclosed in Japanese Patent Publication No. 4-65534. In this technique, a fine wire is obtained by rapidly solidifying an alloy including a main component of Pb, Sn or In and another additional element. The wire is heated to form a ball, and then it is pulled under the condition where the ball is adhered onto an electrode. The wire is thus cut at the base of the ball, resulting in forming a connection structure. Through this structure, a semiconductor device can then be connected, e.g., to the substrate having the electrode thereon and thus possibly to further substrates, components, etc., in a larger operating system. Owing to the use of the aforementioned alloy wire, the wire can be cut at the base of the ball by pulling it after the ball is adhered onto the conductor. However, when the wire is pulled, an electrode or a wire below the ball may be peeled from the substrate, together with the ball before cutting of the wire at the base occurs.
Still another technique is disclosed in Japanese Laid-Open Patent Publication No. 63-122133. In this publication, a method of connecting a semiconductor chip comprising the steps of forming a ball, pressing and adhering the ball onto an electrode, forming a projecting electrode by cutting a wire, and applying pressure to and electrically connecting a semiconductor chip having the projecting electrode to a conductor on a substrate through a member having anisotropic conductivity are disclosed.
In a semiconductor device manufactured in this manner, the semiconductor chip is electrically connected with the substrate through the member having anisotropic conductivity, and hence, there is a fear of a possible current leakage.
Finally, in issued U.S. Pat. Nos. 5,060,844 and 5,147,084, there is defined an electrical interconnection structure wherein a solder portion, e.g., paste, is positioned on a substrate, e.g., on its conductor pad, and a solder ball is then positioned on the paste. The solder ball has a higher melting point than the paste to allow paste reflow without distributing the ball integrity.
It is believed that a new and improved bump connection that can be produced relatively expeditiously on a mass production basis and thus at relatively lower costs than some of the foregoing processes would constitute an advancement in the art.